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I have an Arduino board connected to a Neopixel Ring. This Ring draws more than 0.5 Ampere, so it needs its own power supply (not drawing power via the Arduino board)

I found this schematic that connects a Neopixel and an Arduino to a single power adapter. To my surprise, the power adapter connects its power straight to the 5V pin of the Arduino board.

Arduino seems to advice against this, so my question is: is this the correct way to separately power a device AND an Arduino from one adapter?

enter image description here

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up vote 3 down vote accepted

Yes, it is correct, as long as you leave Arduino unpowered via 9...12 V DC plug, because it will draw power from that 5V adapter.

And of course, be sure your adapter can handle the current for both Arduino and that Ring.

Another option would be to power Arduino as usually. Power the Ring through the 5V adapter. Then join the ground on all devices (Arduino, Ring, 5V supply).

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Yes, but then I would have two power supplies which seems kind of clunky. (like having a lamp with two wall plugs) – Kokodoko Jul 30 '14 at 15:56
@PietBinnenbocht reading the other answer, if you are afraid that reverse voltage will affect regulator, you could add a diode across its output-input pins. Like hqew.net/files/Images/Article/Circuit_Diagram/… – Cornelius Jul 30 '14 at 15:58
I also read the suggestion to take apart a USB cable and use the USB port of the Arduino to connect an adapter. This way you have the benefit of the Arduino's regulator / protection. – Kokodoko Jul 30 '14 at 16:24
@PietBinnenbocht you could build the USB Power Injector from Everyday Practical Electronics epemag3.com/proj/0410.html – Cornelius Jul 30 '14 at 16:31
Wouldn't it be enough to just split the USB cable like this guy is doing? youtube.com/watch?v=PdDRYY-dxRE – Kokodoko Jul 30 '14 at 16:35

By doing this, you are applying 5v to the output of the Arduino's on board voltage regulator. Depending on the regulator model, this pratice could damage it, but in most cases I believe it will not. Assuming the regulator on the arduino board is "ok" with this, the only concern left would be if the AC adapter can supply the current you need.

Another approach would be connecting a 9V adapter to the Arduino power input and use a external regulator to down the voltage to 5V only for supplying the LED's.

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Yes but the problem here is that the LEDS will draw a lot of AMPS, more than the Arduino can handle. Hence the external power source that powers the Arduino board and the Leds separately. – Kokodoko Oct 16 '15 at 11:24

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